For waste clearance management, a conventional waste measurement system can have very high detection efficiency if plastic scintillation detectors are used for measuring the surface activities of wastes, but it will have limited application since such waste measurement systems which use plastic scintillation detectors for activity measurement are incapable of qualitative nuclide identification. On the other hand, although other waste measurement systems that adopt germanium detectors for activity measurement are capable of qualitative nuclide identification, such waste measurement systems can be very pricy and difficult to maintain. Therefore, on the search for better waste measurement system, it is realized that although the systems adopting sodium iodide (NaI) detectors for waste detection might not have satisfactory energy resolution comparing with those systems adopting germanium detectors, the systems using NaI detectors not only can obtain good qualitative nuclide identification, but also can obtain a satisfactory detection efficiency that is even higher than that of the systems adopting germanium detectors. Thus, by performing a specifically designed mathematical calculation upon the energy spectrum obtained from the systems using NaI detectors, the nuclide identification ability of such systems using NaI detectors can be improved to an extend that they are fully capable of being used for waste clearance management. Moreover, in addition to the advantages of low-cost and ease-to-maintain in the NaI detector, it can also operate smoothly without the requirement for using liquid nitrogen in thermostatic control as the germanium detector did. Consequently, it is becoming a good idea for applying NaI detectors in systems of waste clearance management.
Please refer to FIG. 1, which is a schematic diagram showing an energy spectrum of prior art. As shown in FIG. 1, the energy spectrum A relating to a nuclide A is located near to the energy spectrum B relating to a nuclide B, and thus, by adding the two energy spectrums together, a larger energy spectrum can be constructed, i.e. the energy spectrum A+B. Conventionally, the type of a nuclide is identified and determined based upon the horizontal channel position corresponding to the peak of the energy spectrum that is shown in FIG. 1. Therefore, using the conventional nuclide identification method, it is unable to recognize that the joint energy spectrum A+B is actually the combination of the energy spectrum A relating to a nuclide A and the energy spectrum B relating to a nuclide B, and consequently, an erroneous nuclide identification of one erroneous nuclide instead of two correct nuclides is made as it can only identify one peak from the joint energy spectrum A+B.